1. Field of the Invention
The embodiment of the present invention relates to a signal output circuit, optical pickup and optical device for outputting a signal onto a transmission line having a given transmission characteristic.
2. Description of the Related Art
An optical disk pickup has to convey a signal to the signal processor at the subsequent stage via a relatively long flexible cable whose transmission characteristic varies from one product to another.
Therefore, elaborately thought-out ideas are desired at the output end of the transmitting circuit (IC), including addition of an optimal damping resistor for the flexible cable.
Signal transmission from the pickup to the IC at the subsequent stage has been optimized by adding a chip resistor to the output end of the IC incorporated in the pickup.
Media such as CD and DVD in high speed mode, BD and HD-DVD desire a signal band of 100 MHz or higher. A signal deteriorates if transmitted via FPC (Flexible Printed Circuit), FFC (Flat Flexible Cable) or other flexible transmission line.
Therefore, optical pickups available today have an external resistor (damping resistor) to adjust the transmission waveform, thus suppressing the resonance of the FPC and FFC and providing a more or less flat transmission characteristic at a frequency around 100 MHz.
FIG. 1 is an equivalent circuit diagram of the signal transmission system in a typical optical pickup.
In this circuit, a resistor Rd is externally added to the output side of the output circuit which is the transmitting IC of the optical pickup.
The resistance of the resistor Rd is adjusted to be optimal for a transmission line 2 such as flexible cable and an IC 3 at the subsequent stage.
This technique can ensure optimal transmission (suppress the peaking of the flexible transmission line) to a certain extent.